1. Field of Invention
The present invention relates to a field of permanent magnetic materials, and more particularly to a method for producing neodymium-iron-boron rare earth permanent magnetic materials.
2. Description of Related Arts
Neodymium-iron-boron rare earth permanent magnetic materials are widely applied in the nuclear magnetic resonance imaging of medical industry, hard disk drivers of computers, loudspeaker boxes, mobiles, etc., because of its excellent magnetic property. To meet the requirements of energy-saving and the low carbon economy, the neodymium-iron-boron rare earth permanent magnetic materials are applied in fields of automobile parts, household appliances, energy-saving and controlling motors, hybrid electric vehicles, wind power generation, etc.
In 1982, Japan Sumitomo Special Metals Co. firstly disclosed the neodymium-iron-boron rare earth permanent magnetic materials in Japanese patents 1,622,492 and 2,137,496, and then applied for United States patents and European patents. The characteristic, ingredients, and producing method of the neodymium-iron-boron rare earth permanent magnetic materials were disclosed. The main phase is Nd2Fe14B phase, and the grain boundary phases are Nd-rich phase, B-rich phase, and impurities comprising rare earth oxides.
On Apr. 1, 2007, Japan Hitachi Metals Co. was merged with Japan Sumitomo Special Metals Co., and took up the rights and obligations of the patent licenses of the neodymium-iron-boron rare earth permanent magnetic materials of Japan Sumitomo Special Metals Co. on Aug. 17, 2012, Japan Hitachi Metals Co. submitted a case to United States International Trade Commission (ITC), based on the fact that Japan Hitachi Metals Co. owns the patents U.S. Pat. Nos. 6,461,565, 6,491,765, 6,537,385, and 6,527,874 applied in United States.
The patent U.S. Pat. No. 6,461,565 has an application date of May 8, 2001, and the application number in China is CN1195600C. It is recorded in the patent that magnetic compaction is not easy to be realized in a protective atmosphere, so magnetic compaction in an atmospheric condition was applied to be protected, wherein the working temperature range is 5° C.˜30° C., the relative humidity is between 40% and 65%, and the powder compacting is processed under the conditions described above.
Based on the patent U.S. Pat. No. 6,491,765 applied on May 9, 2001, and the patent U.S. Pat. No. 6,537,385 applied on Jul. 9, 2001, a patent CN1272809C is applied in China. A milling process finished by an inert gas jet mill having an oxygen content of 0.02˜5% is protected by the patents, wherein a part of ultrafine powder having a grain diameter less than 1 μm is removed by a cyclone collector, in such a manner that the proportion of the ultrafine powder having the grain diameter less than 1 μm is controlled under 10%. It is a natural process that a part of ultrafine powder having the grain diameter less than 1 μm is removed, because the cyclone collector is used to collect the powder combined with the jet mill.
Strip casting technology related to smelting process of neodymium-iron-boron rare earth permanent magnetic alloys comprising at least one of the metal elements Nb and Mo is required to be protected in the patent U.S. Pat. No. 6,527,874 applied on Jul. 10, 2001 by Japan Hitachi Metals Co., and the Chinese patent CN1182548C. The strip casting technology was used in smelting process sintering magnets by Japan SanDe Metal Co. in 1992. The Japanese patent JP4,028,656 was granted in United States in January of 1995, and the patent number is U.S. Pat. No. 5,383,978. Then it was granted in Europe, and the patent numbers are EP0556751B1 and EP0632471B1.
The conventional method for producing neodymium-iron-boron rare earth permanent magnetic materials comprises: alloy smelting, hydrogen pulverization, milling by the jet mill, magnetic compaction, vacuum sintering, mechanical processing and aging process.